1. Field of the Invention
The present invention relates to methods for manufacturing color filters, which are components of color liquid crystal displays for use in color TVs, personal computers, and the like, and it relates to liquid crystal elements using the color filters manufactured thereby.
2. Description of the Related Art
Recently, concomitant with progress in personal computers, particularly, progress in portable personal computers, liquid crystal displays, in particular, color liquid crystal displays, are in increasing demand. However, it is inevitably necessary to reduce the cost thereof to further broaden applications thereof, and specifically, cost reduction of color filters, which are relatively expensive, has been desired.
Accordingly, in order to fulfill the desires described above, development of manufacturing methods for color filters exploiting inkjet printing techniques has been actively pursued (Japanese Patent Laid-Open Nos. 59-75205, 63-235901, and 1-217,320). The inventors of the present invention also proposed a method for forming coloring portions of red (R), green (G), and blue (B) using an inkjet printing technique in Japanese Patent Nos. 2,872,594, 2,872,595, 2,872,596, and the like.
Conventionally, a manufacturing method for a liquid crystal element comprises a step of providing liquid crystal driving units such as thin-film transistors (TFTS) and a coloring optical element such as a color filter on respective glass substrate, which are a pair of transparent insulating substrates, and a step of forming a transparent electrode and an alignment film on each substrate. Next, substantial spheres or cylindrical particles 3 to 10 .mu.m in diameter composed of silica, alumina, a synthetic resin, or the like are dispersed as spacers on the entire surface of one glass substrate provided with the transparent electrode and the alignment film. The two glass substrates are adhered to each other so that each transparent electrode opposes the other with the spacers in a gap therebetween, and a liquid crystal is contained in the gaps between the glass substrates, whereby a liquid crystal element is formed.
However, since recent further miniaturization and finer processing of liquid crystal displays have been significant, in addition to the need for cost reduction thereof, improvement in display reliability has also been necessary more than ever. As one of the reasons for display defects in liquid crystal displays, non-uniformity of cell gaps (thickness of the liquid crystal layer) may be mentioned. Generally, in order to make cell gaps uniform, spacers are used which are uniformly dispersed between substrates containing a liquid crystal therebetween. However, when spacers are not uniformly dispersed, the thickness of a part of the liquid crystal layer varies, so that display defects may occur. In addition, when spacers partly agglomerate, light is scattered, so that display defects may also occur.
In general, beads of resin or silica, glass fibers, or the like are used as spacers, and they are uniformly dispersed on the substrate by the following methods. (1) A method in which spacers are uniformly dispersed in a low boiling point solvent, such as a flon or an alcohol, using ultrasonic waves or the like, and the solvent is then removed after atomizing the solution on the substrate. (2) A method in which spacers are dispersed on the substrate utilizing static electricity or an airstream.
However, when the methods described above are used, since spacers are randomly dispersed on the substrate, they are also disposed on pixels of R, G, and B, resulting in display defects. In particular, in the methods described above, agglomeration of spacers is not totally avoided, so that light is scattered by partial agglomerates of spacers, resulting in display defects.
In order to solve the problems described above, methods are proposed in Japanese Patent Laid-Open Nos. 61-173221, 2-223922, and the like, in which, after an alignment film is processed for rubbing, spacers composed of a polyimide or a resist are formed at places other than effective pixels by exposing a photosensitive polyimide or photoresist coated beforehand using a mask. According to the method described above, since spacers can be formed at desired places at desired density, non-uniformity of liquid crystal cell gaps can be improved when liquid crystal is contained therein. In addition, in Japanese Patent Laid-Open No. 3-94230, a method for fixing spacers in the form of beads on a shading layer in an area other than effective pixels is disclosed.
Furthermore, a method for using a thick black matrix as spacers disclosed in Japanese Patent Laid-Open Nos. 63-237032, 3-184022, 4-122914, and the like, a method for using an overlapped color resist as spacers disclosed in Japanese Patent Laid-Open No. 63-82405, and a method for forming a coloring pattern on a black matrix so as to be spacers disclosed in Japanese Patent Laid-Open No. 63-237032 have been proposed.
However, in order to form spacers having a uniform height on a large substrate, the thickness of a photosensitive resin composition to be coated on the substrate must be strictly controlled. In addition, when surface flatness of an underlying substrate is poor, there is a problem in that the thickness control mentioned above is difficult.